The present invention relates to a shell structure having a force transmission point.
It is known to provide in components made of carbon fiber-reinforced plastic (CFRP), which are produced in a shell structure, force transmission points by connection elements integrated in the CFRP, such as a laminated nut. This process is connected with high expenditures of time and, as a rule, permits no subsequent change. In other words, after the lamination operation has been concluded, it will no longer be possible to integrate a connection element in the component. As a result, this process can currently not be presented with the required cycle time in component manufacturing for series production.
From the manufacturing of steel or aluminum vehicle bodies, it is known to implement screwed connections with a higher strength class by means of press-fit elements or welded elements (press-fit stud, press nut, weld stud, weld nut). In the case of CFRP components, this is often not possible because of high contact corrosion and limitations with respect to the permissible seating stress.
From German Patent Document DE 103 05 015 A1, a force transmission device is known for the fixing in or on a structural component as well as a structural component constructed by using at least one such force transmission device, which structural component is constructed for improving the mechanical characteristics and for a more cost-effective manufacturing as a hybrid component, with an insert made of metal, which is fixed in a structure made of plastic, the structure being designed for the fixing, for example, gluing into a recess, such as a plate-shaped impressing, of the structural component. The production of the fixing structure as well as the providing of the recess at the component require comparatively high expenditures. As a result of the recess, an elevated structure is created on the visible side of the component, which may be objectionable for esthetic and/or constructive reasons. Since the lateral dimension of the fixing structure is also limited for reasons of weight, the force transmission is comparatively punctiform and the forces that can be transmitted are limited. In addition, moisture may possibly penetrate into the interior of the component through the threaded hole.
It is an object of the present invention to provide a shell structure having a force transmission point which at least partly avoids the disadvantages of the prior art. In particular, it is an object of the present invention to create a force transmission structure on CFRP components with higher strength, with a lower probability of damaging the latter, while reducing corrosive disadvantages and with a distributed force transmission into the CFRP component for an industrialized application with high piece numbers. It is a further object of the invention to simplify a force transmission structure with respect to construction and manufacturing and to permit greater transmissible forces. Another further object of the invention consists of making the penetration of moisture through the force transmission point more difficult.
According to the invention, a shell structure is suggested which has a force transmission point, a force transmission structure being provided at the force transmission point, the force transmission structure having a fitting part with a fastening element, the fitting part being connected with the shell structure, and, in addition, the fitting part has a contact surface with the shell structure and the contact surface can be braced or is braced with the shell structure.
For the purpose of the invention, a shell structure is a structure that is part of a surface-type, curved or plane or partially curved and partially plane formation. Surface-type means that the structure thickness is much smaller than the remaining dimensions. For the purpose of the invention a force transmission structure is a structure which is designed and established for absorbing forces and guiding them into the shell structure. For the purpose of the invention, a fitting part is a spatial shape which provides the force transmission structure with dimension and stability. For the purpose of the invention, a fastening element is a device which is used for fastening a component, by way of which force is guided into the force transmission structure. For the purpose of the invention, a contact surface having the shell structure is to be understood such that the contact surface rests flatly against the shell structure. Flatly resting against the shell structure means that no elastic intermediate layers, such as an adhesive or the like, are present between the contact surface and the shell structure.
However, it is conceivable that a thin, at least essentially inelastic intermediate layer is provided, for example, for insulation purposes, for protection against corrosion or for transferring mechanical power, an inelastic intermediate layer being an intermediate layer which, when loaded by pressure, in comparison to the load transmission part or the shell structure, has an essentially insignificant deformation trajectory to being totally deformed. This means that here material properties, such as the modulus of elasticity, are not as important as the deformation path, which may be negligible in the case of an extremely thin intermediate layer. Such an intermediate layer may, for example, be a paint layer, a paper layer or plastic film. In other words, the resting against the shell structure should at least essentially permit a direct force transmission between the contact surface and the shell structure. Bracing the contact surface with the shell structure means that the contact surface is pressed firmly against the shell structure. This can, for example but not exclusively, be achieved by a screwed connection, a toggle closure, a wedging or other means. As a result of the resting against the shell structure and the bracing of the contact surface, a defined force transmission is implemented, and angular deviations can be avoided. The force is transmitted by way of a large surface, which reduces the surface pressure and, especially in the case of thin shell structures, reduces tensions to a bearable extent and thereby permits higher transmissible forces.
The invention is particularly advantageously applicable to a shell structure produced of fiber-reinforced plastic, particularly glass fiber-reinforced plastic (GFRP) or CFRP. Particularly in the case of fiber-reinforced plastics, the pulling-out risk of force transmission points is high, so that they can profit considerably from the invention.
In an embodiment of the invention the fitting part is made of metal, particularly iron or steel or aluminum or of an alloy with at least one of these metals. Particularly in the case of CFRP components, a problem often occurs concerning the contact corrosion with metals, which can be effectively reduced by the bracing and firm contact on the contact surface.
In a further embodiment of the invention, the fitting part is a sheet-shaped, plate-shaped or disk-shaped component, in which case the contact surface is caused by cold forming or cranking. Such manufacturing processes can be cost-effectively implemented and can be used in large-scale and mass production. As an alternative, the fitting part may also be a more massive, for example, but not exclusively, cast component with a turned-off, milled-off, planed-off or stripped shoulder, which forms the contact surface.
In a further embodiment of the invention, the fitting part is glued to the shell structure, in which case, the contact surface is free of adhesive. By means of the glued connection, the fitting part can be fixed at the desired location already before the bracing, which facilitates manufacturing. An additional stiffening of the shell structure and a further force transmission can also be achieved, which is distributed over a larger surface. Because the contact surface is free of adhesive, the positioning and bracing can also take place with high locating and positioning precision. When the gluing-together takes place in a large-surface and circumferential manner, a good sealing effect of the force transmission point can also be achieved.
In a further embodiment of the invention, the fitting part or the shell structure has a surface that juts back from the contact surface, which jutting-back is used for the gluing to the shell structure. When the shell structure has the jutting-back surface, the fitting part may have a simpler and less costly design. Since the production of the shell structure usually requires the production of a mold anyhow, a jutting-back surface or, inversely, a surface jutting forward to the fitting part may also be provided there. When the fitting part has the jutting-back surface, the component surface of the shell structure may be kept smooth. Also, the projection does not have to be provided in the mold, which also permits a subsequent providing of force transmitting points after the lamination of the shell structure. At the fitting part, the jutting-back surface may, for example, but not exclusively, be produced by a cold forming process, such as a deep-drawing process.
When the jutting-back surface forms a gap with the surface of the shell structure opposite the jutting-back surface at least in the area of the glued connection, which gap at least essentially has a uniform distance, the adhesive force can also be provided in a uniform manner.
The design can provide that the contact surface is at least essentially plane. This also requires that the opposite area of the shell structure is also plane in this area. By means of a plane surface, an axis position of the force transmission structure can also be precisely defined.
In a further embodiment of the invention. Thus, a visible side of the shell structure which faces the public, can be differentiated from a fitting side on which the fitting part is mounted. Thus, the visible side can be kept free of annoying elements, in which case, essentially only necessary linking points for the force transmission are provided on the visible side.
In a further embodiment of the invention, the contact surface is braced by way of the fastening element with a surface of the shell structure. This means that the fastening element is provided in the area of the contact surface. As a result, the fastening element is fixed in its location and position. The fastening element is also used for bracing the contact surface with the shell structure, so that no additional means are to be provided for the bracing.
As an alternative, it is conceivable to carry out the bracing by completely different means and to use the fastening element exclusively for the absorption of force.
In a further embodiment of the invention, the fastening element has a threaded element which is provided at the fitting part. For the purpose of the invention, a threaded element is a component which is connected with the fitting part or is integrated in it and has an internal or external thread or an internal thread formed therein or an external thread formed thereon.
In a further embodiment of the invention, the threaded element is fastened to the fitting part from a side of the fitting part situated opposite the contact surface, preferably connected with the fitting part, particularly pressed into a through hole formed in the fitting part. The threaded element can therefore be mounted where it has no negative effect.
When the threaded element has a bolt part, it is preferably designed such that the bolt part projects through an opening in the shell structure. When the threaded element has an internal thread, it is preferably designed such that it does not project beyond the contact surface. In the latter case, it is advantageous for the threaded element or the internal thread to be accessible through and opening in the shell structure. These two embodiment alternatives ensure that the threaded element is accessible and can be used from the visible side of the shell structure.
In a further embodiment of the invention, the fastening element has a press nut which, from a side of the fitting part situated opposite the contact surface, is pressed into a through hole designed in a section of the fitting part corresponding to the contact surface, and which does not project beyond the contact surface, wherein, by means of a screw, which is to be guided through an opening in the shell structure aligned with the press nut into the press nut, the contact surface can be braced or is braced with the shell structure, wherein by means of the screw, simultaneously a load absorption element for absorbing an external load can be fixed or is fixed on a side of the shell structure situated opposite the fitting part. This screwed connection concept permits more stable screwed connections with CFRP components without damaging them and without corrosive disadvantages and with a flat force transmission into the CFRP component for the industrialized application with high piece numbers.
In an advantageous further development of the invention, a covering is provided which covers the fitting part, the covering preferably being glued to that of the shell structure in a circumferential fashion. As a result, moisture which may possibly penetrate at the location of the force transmission point from the visible side onto the back side, can be caught and can also not contaminate a cavity which is closed off by the shell structure.
Particularly advantageously, the invention is, however, not exclusively applicable to a shell structure which is a vehicle body part, particularly of a motor vehicle.
Further characteristics, objects and effects of the invention are contained in the description and in the attached drawing. In this case, characteristics and details, which are described in connection with the device according to the invention, naturally also apply in connection with all modifications and in each case inversely and reciprocally, so that with respect to the disclosure of individual aspects and forms of the invention, reference is made or can always made reciprocally.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawing.